Method and apparatus for transmitting and receiving wireless signal in wireless communication system

ABSTRACT

The present invention relates to a wireless communication system and, more particularly, to a method comprising the steps of: generating a first complex symbol sequence corresponding to one time unit including a plurality of transmission symbols; generating a second complex symbol sequence by applying primary scrambling to the first complex symbol sequence on a modulation symbol basis; and repeatedly transmitting the second complex symbol sequence through a plurality of time units, wherein secondary scrambling is applied to the signals in each time unit on a transmission symbol basis, the transmission symbol including an OFDMA symbol or an SC-FDMA symbol; and an apparatus therefor.

This application is the National Stage filing under 35 U.S.C. 371 ofInternational Application No. PCT/KR2018/007306 filed Jun. 27, 2018,which claims the benefit of U.S. Provisional Application Nos. 62/525,727filed Jun. 27, 2017; 62/528,518 filed Jul. 4, 2017; 62/547,772 filedAug. 19, 2017 and 62/548,919 filed Aug. 22, 2017, the contents of whichare all hereby incorporated by reference herein in their entirety.

TECHNICAL FIELD

The present disclosure relates to a wireless communication system and,more particularly, to a method and apparatus for transmitting andreceiving a radio signal. The wireless communication system includes anarrowband Internet of Things (NB-IoT)-based wireless communicationsystem.

BACKGROUND ART

Generally, a wireless communication system is developing to diverselycover a wide range to provide such a communication service as an audiocommunication service, a data communication service and the like. Thewireless communication is a sort of a multiple access system capable ofsupporting communications with multiple users by sharing availablesystem resources (e.g., bandwidth, transmit power, etc.). For example,the multiple access system may include one of CDMA (code divisionmultiple access) system, FDMA (frequency division multiple access)system, TDMA (time division multiple access) system, OFDMA (orthogonalfrequency division multiple access) system, SC-FDMA (single carrierfrequency division multiple access) system and the like.

DETAILED DESCRIPTION OF THE DISCLOSURE Technical Problems

An object of the present disclosure is to provide a method ofefficiently performing a radio signal transmission and reception processand an apparatus therefor.

The objects that can be achieved with the present disclosure are notlimited to what has been particularly described hereinabove and otherobjects not described herein will be more clearly understood by personsskilled in the art from the following detailed description.

Technical Solutions

According to an aspect of the present disclosure, provided herein is amethod of transmitting a signal by a base station (BS) in a wirelesscommunication system, including generating a first complex symbolsequence related with one time unit including a plurality oftransmission symbols; generating a second complex symbol sequence byapplying primary scrambling to the first complex symbol sequence inunits of modulation symbols; and repeatedly transmitting the secondcomplex symbol sequence through a plurality of time units, secondaryscrambling being applied to a signal in each time unit in units oftransmission symbols, wherein the transmission symbols includeorthogonal frequency division multiplexing (OFDM) symbols orsingle-carrier frequency division multiple access (SC-FDMA) symbols.

In another aspect of the present disclosure, provided herein is a userequipment (UE) used in a wireless communication system, including aradio frequency (RF) module; and a processor, wherein the processor isconfigured to generate a first complex symbol sequence related with onetime unit including a plurality of transmission symbols, generate asecond complex symbol sequence by applying primary scrambling to thefirst complex symbol sequence in units of modulation symbols, andrepeatedly transmit the second complex symbol sequence through aplurality of time units, secondary scrambling being applied to a signalin each time unit in units of transmission symbols, and wherein thetransmission symbols include orthogonal frequency division multiplexing(OFDM) symbols or single-carrier frequency division multiple access(SC-FDMA) symbols.

The second complex symbol sequence may be transmitted through anarrowband physical downlink control channel (NPDCCH), a narrowbandphysical downlink shared channel (NPDSCH), or a narrowband physicaluplink shared channel (NPUSCH).

The time unit may include a slot

The secondary scrambling may include adding one value among a pluralityof complex values, for example, {1, −1, j, −j}, in units of OFDM symbolsto the signal in each time unit in the form of multiplication.

The second complex symbol sequence may be transmitted through 1, 3, 6,or 12 subcarriers in each time unit.

The signal in each time unit may be changed in order in units of thetransmission symbols.

The wireless communication system may include a wireless communicationsystem supporting narrowband Internet of Things (NB-IoT)

Advantageous Effects

According to the present disclosure, wireless signal transmission andreception can be efficiently performed in a wireless communicationsystem.

Effects obtainable from the present disclosure may be non-limited by theabove mentioned effect. And, other unmentioned effects can be clearlyunderstood from the following description by those having ordinary skillin the technical field to which the present disclosure pertains.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the disclosure and are incorporated in and constitute apart of this specification, illustrate embodiments of the disclosure andtogether with the description serve to explain the principles of thedisclosure.

FIG. 1 illustrates physical channels used in 3GPP LTE(-A) and a signaltransmission method using the same.

FIG. 2 illustrates a radio frame structure.

FIG. 3 illustrates a resource grid of a downlink slot.

FIG. 4 illustrates a downlink subframe structure.

FIG. 5 illustrates the structure of an uplink subframe used in LTE(-A).

FIG. 6 illustrates the structure of a self-contained subframe.

FIG. 7 illustrates a frame structure defined in 3GPP NR.

FIG. 8 illustrates deployment of an in-band anchor carrier in an LTEbandwidth of 10 MHz.

FIG. 9 illustrates locations at which NB-IoT DL physicalchannels/signals are transmitted in an FDD LTE system.

FIG. 10 illustrates resource allocation of an NB-IoT signal and an LTEsignal in an in-band mode.

FIG. 11 illustrates a scrambling initialization method of a narrowbandphysical downlink shared channel (NPDSCH) not carrying broadcast controlchannel (BCCH) data.

FIG. 12 illustrates narrowband physical broadcast channel (NPBCH)transmission.

FIG. 13 illustrates a system model for explaining a scrambling scheme.

FIGS. 14 to 16 illustrate signal transmission according to the presentdisclosure.

FIG. 17 illustrates a base station and a user equipment applicable to anembodiment of the present disclosure.

BEST MODE FOR CARRYING OUT THE DISCLOSURE

Embodiments of the present disclosure are applicable to a variety ofwireless access technologies such as code division multiple access(CDMA), frequency division multiple access (FDMA), time divisionmultiple access (TDMA), orthogonal frequency division multiple access(OFDMA), and single carrier frequency division multiple access(SC-FDMA). CDMA can be implemented as a radio technology such asUniversal Terrestrial Radio Access (UTRA) or CDMA2000. TDMA can beimplemented as a radio technology such as Global System for Mobilecommunications (GSM)/General Packet Radio Service (GPRS)/Enhanced DataRates for GSM Evolution (EDGE). OFDMA can be implemented as a radiotechnology such as Institute of Electrical and Electronics Engineers(IEEE) 802.11 (Wireless Fidelity (Wi-Fi)), IEEE 802.16 (Worldwideinteroperability for Microwave Access (WiMAX)), IEEE 802.20, and EvolvedUTRA (E-UTRA). UTRA is a part of Universal Mobile TelecommunicationsSystem (UMTS). 3rd Generation Partnership Project (3GPP) Long TermEvolution (LTE) is a part of Evolved UMTS (E-UMTS) using E-UTRA,employing OFDMA for downlink and SC-FDMA for uplink. LTE-Advanced(LTE-A) evolves from 3GPP LTE. While the following description is given,centering on 3GPP LTE/LTE-A for clarity, this is purely exemplary andthus should not be construed as limiting the present disclosure.

In a wireless communication system, a user equipment (UE) receivesinformation through downlink (DL) from a base station (BS) and transmitinformation to the BS through uplink (UL). The information transmittedand received by the BS and the UE includes data and various controlinformation and includes various physical channels according totype/usage of the information transmitted and received by the UE and theBS.

FIG. 1 illustrates physical channels used in 3GPP LTE(-A) and a signaltransmission method using the same.

When powered on or when a UE initially enters a cell, the UE performsinitial cell search involving synchronization with a BS in step S101.For initial cell search, the UE synchronizes with the BS and acquireinformation such as a cell Identifier (ID) by receiving a primarysynchronization channel (P-SCH) and a secondary synchronization channel(S-SCH) from the BS. Then the UE may receive broadcast information fromthe cell on a physical broadcast channel (PBCH). In the mean time, theUE may check a downlink channel status by receiving a downlink referencesignal (DL RS) during initial cell search.

After initial cell search, the UE may acquire more specific systeminformation by receiving a physical downlink control channel (PDCCH) andreceiving a physical downlink shared channel (PDSCH) based oninformation of the PDCCH in step S102.

The UE may perform a random access procedure to access the BS in stepsS103 to S106. For random access, the UE may transmit a preamble to theBS on a physical random access channel (PRACH) (S103) and receive aresponse message for preamble on a PDCCH and a PDSCH corresponding tothe PDCCH (S104). In the case of contention-based random access, the UEmay perform a contention resolution procedure by further transmittingthe PRACH (S105) and receiving a PDCCH and a PDSCH corresponding to thePDCCH (S106).

After the foregoing procedure, the UE may receive a PDCCH/PDSCH (S107)and transmit a physical uplink shared channel (PUSCH)/physical uplinkcontrol channel (PUCCH) (S108), as a general downlink/uplink signaltransmission procedure. Control information transmitted from the UE tothe BS is referred to as uplink control information (UCI). The UCIincludes hybrid automatic repeat and requestacknowledgement/negative-acknowledgement (HARQ-ACK/NACK), schedulingrequest (SR), channel state information (CSI), etc. The CSI includes achannel quality indicator (CQI), a precoding matrix indicator (PMI), arank indicator (RI), etc. While the UCI is transmitted on a PUCCH ingeneral, the UCI may be transmitted on a PUSCH when control informationand traffic data need to be simultaneously transmitted. In addition, theUCI may be aperiodically transmitted through a PUSCH according torequest/command of a network.

FIG. 2 illustrates a radio frame structure. Uplink/downlink data packettransmission is performed on a subframe-by-subframe basis. A subframe isdefined as a predetermined time interval including a plurality ofsymbols. 3GPP LTE supports a type-1 radio frame structure applicable tofrequency division duplex (FDD) and a type-2 radio frame structureapplicable to time division duplex (TDD).

FIG. 2(a) illustrates a type-1 radio frame structure. A downlinksubframe includes 10 subframes each of which includes 2 slots in thetime domain. A time for transmitting a subframe is defined as atransmission time interval (TTI). For example, each subframe has aduration of 1 ms and each slot has a duration of 0.5 ms. A slot includesa plurality of OFDM symbols in the time domain and includes a pluralityof resource blocks (RBs) in the frequency domain. Since downlink usesOFDM in 3GPP LTE, an OFDM symbol represents a symbol period. The OFDMsymbol may be called an SC-FDMA symbol or symbol period. An RB as aresource allocation unit may include a plurality of consecutivesubcarriers in one slot.

The number of OFDM symbols included in one slot may depend on cyclicprefix (CP) configuration. CPs include an extended CP and a normal CP.When an OFDM symbol is configured with the normal CP, for example, thenumber of OFDM symbols included in one slot may be 7. When an OFDMsymbol is configured with the extended CP, the length of one OFDM symbolincreases, and thus the number of OFDM symbols included in one slot issmaller than that in case of the normal CP. In case of the extended CP,the number of OFDM symbols allocated to one slot may be 6. When achannel state is unstable, such as a case in which a UE moves at a highspeed, the extended CP can be used to reduce inter-symbol interference.

When the normal CP is used, one subframe includes 14 OFDM symbols sinceone slot has 7 OFDM symbols. The first three OFDM symbols at most ineach subframe can be allocated to a PDCCH and the remaining OFDM symbolscan be allocated to a PDSCH.

FIG. 2(b) illustrates a type-2 radio frame structure. The type-2 radioframe includes 2 half frames. Each half frame includes 4(5) normalsubframes and 10 special subframes. The normal subframes are used foruplink or downlink according to UL-DL configuration. A subframe iscomposed of 2 slots.

Table 1 shows subframe configurations in a radio frame according toUL-DL configurations.

TABLE 1 Uplink- Downlink- downlink to-Uplink config- Switch pointSubframe number uration periodicity 0 1 2 3 4 5 6 7 8 9 0 5 ms D S U U UD S U U U 1 5 ms D S U U D D S U U D 2 5 ms D S U D D D S U D D 3 10 ms D S U U U D D D D D 4 10 ms  D S U U D D D D D D 5 10 ms  D S U D D D DD D D 6 5 ms D S U U U D S U U D

In Table 1, D denotes a downlink subframe, U denotes an uplink subframeand S denotes a special subframe. The special subframe includes DwPTS(Downlink Pilot TimeSlot), GP (Guard Period), and UpPTS (Uplink PilotTimeSlot). DwPTS is used for initial cell search, synchronization orchannel estimation in a UE and UpPTS is used for channel estimation in aBS and uplink transmission synchronization in a UE. The GP eliminates ULinterference caused by multi-path delay of a DL signal between a UL anda DL.

The radio frame structure is merely exemplary and the number ofsubframes included in the radio frame, the number of slots included in asubframe, and the number of symbols included in a slot can be vary.

FIG. 3 illustrates a resource grid of a downlink slot.

Referring to FIG. 3, a downlink slot includes a plurality of OFDMsymbols in the time domain. While one downlink slot may include 7 OFDMsymbols and one resource block (RB) may include 12 subcarriers in thefrequency domain in the figure, the present disclosure is not limitedthereto. Each element on the resource grid is referred to as a resourceelement (RE). One RB includes 12×7 REs. The number NRB of RBs includedin the downlink slot depends on a downlink transmit bandwidth. Thestructure of an uplink slot may be same as that of the downlink slot.

FIG. 4 illustrates a downlink subframe structure.

Referring to FIG. 4, a maximum of three (four) OFDM symbols located in afront portion of a first slot within a subframe correspond to a controlregion to which a control channel is allocated. The remaining OFDMsymbols correspond to a data region to which a physical downlink sharedchancel (PDSCH) is allocated. A basic resource unit of the data regionis an RB. Examples of downlink control channels used in LTE include aphysical control format indicator channel (PCFICH), a physical downlinkcontrol channel (PDCCH), a physical hybrid ARQ indicator channel(PHICH), etc. The PCFICH is transmitted at a first OFDM symbol of asubframe and carries information regarding the number of OFDM symbolsused for transmission of control channels within the subframe. The PHICHis a response of uplink transmission and carries a HARQ acknowledgment(ACK)/negative-acknowledgment (NACK) signal. Control informationtransmitted through the PDCCH is referred to as downlink controlinformation (DCI). The DCI includes uplink or downlink schedulinginformation or an uplink transmit power control command for an arbitraryUE group.

Control information transmitted through the PDCCH is referred to asdownlink control information (DCI). Formats 0, 3, 3A and 4 for uplinkand formats 1, 1A, 1B, 1C, 1D, 2, 2A, 2B and 2C for downlink are definedas DCI formats. Information field type, the number of informationfields, the number of bits of each information field, etc. depend on DICformat. For example, the DCI formats selectively include informationsuch as hopping flag, RB assignment, MCS (Modulation Coding Scheme), RV(Redundancy Version), NDI (New Data Indicator), TPC (Transmit PowerControl), HARQ process number, PMI (Precoding Matrix Indicator)confirmation as necessary. Accordingly, the size of control informationmatched to a DCI format depends on the DCI format. An arbitrary DCIformat may be used to transmit two or more types of control information.For example, DIC formats 0/1A is used to carry DCI format 0 or DICformat 1, which are discriminated from each other using a flag field.

A PDCCH may carry a transport format and a resource allocation of adownlink shared channel (DL-SCH), resource allocation information of anuplink shared channel (UL-SCH), paging information on a paging channel(PCH), system information on the DL-SCH, information on resourceallocation of an upper-layer control message such as a random accessresponse transmitted on the PDSCH, a set of Tx power control commands onindividual UEs within an arbitrary UE group, a Tx power control command,information on activation of a voice over IP (VoIP), etc. A plurality ofPDCCHs can be transmitted within a control region. The UE can monitorthe plurality of PDCCHs. The PDCCH is transmitted on an aggregation ofone or several consecutive control channel elements (CCEs). The CCE is alogical allocation unit used to provide the PDCCH with a coding ratebased on a state of a radio channel. The CCE corresponds to a pluralityof resource element groups (REGs). A format of the PDCCH and the numberof bits of the available PDCCH are determined by the number of CCEs. TheBS determines a PDCCH format according to DCI to be transmitted to theUE, and attaches a cyclic redundancy check (CRC) to control information.The CRC is masked with a unique identifier (referred to as a radionetwork temporary identifier (RNTI)) according to an owner or usage ofthe PDCCH. If the PDCCH is for a specific UE, a unique identifier (e.g.,cell-RNTI (C-RNTI)) of the UE may be masked to the CRC. Alternatively,if the PDCCH is for a paging message, a paging identifier (e.g.,paging-RNTI (P-RNTI)) may be masked to the CRC. If the PDCCH is forsystem information (more specifically, a system information block(SIB)), a system information RNTI (SI-RNTI) may be masked to the CRC.When the PDCCH is for a random access response, a random access-RNTI(RA-RNTI) may be masked to the CRC.

The PDCCH carries a message known as DCI which includes resourceassignment information and other control information for a UE or UEgroup. In general, a plurality of PDCCHs can be transmitted in asubframe. Each PDCCH is transmitted using one or more CCEs. Each CCEcorresponds to 9 sets of 4 REs. The 4 REs are referred to as an REG. 4QPSK symbols are mapped to one REG. REs allocated to a reference signalare not included in an REG, and thus the total number of REGs in OFDMsymbols depends on presence or absence of a cell-specific referencesignal. The concept of REG (i.e. group based mapping, each groupincluding 4 REs) is used for other downlink control channels (PCFICH andPHICH). That is, REG is used as a basic resource unit of a controlregion. 4 PDCCH formats are supported as shown in Table 2.

TABLE 2 PDCCH Number of Number Number of PDCCH format CCEs (n) of REGsbits 0 1 9 72 1 2 8 144 2 4 36 288 3 5 72 576

CCEs are sequentially numbered. To simplify a decoding process,transmission of a PDCCH having a format including n CCEs can be startedusing as many CCEs as a multiple of n. The number of CCEs used totransmit a specific PDCCH is determined by a BS according to channelcondition. For example, if a PDCCH is for a UE having a high-qualitydownlink channel (e.g. a channel close to the BS), only one CCE can beused for PDCCH transmission. However, for a UE having a poor channel(e.g. a channel close to a cell edge), 8 CCEs can be used for PDCCHtransmission in order to obtain sufficient robustness. In addition, apower level of the PDCCH can be controlled according to channelcondition.

LTE defines CCE positions in a limited set in which PDCCHs can bepositioned for each UE. CCE positions in a limited set that the UE needsto monitor in order to detect the PDCCH allocated thereto may bereferred to as a search space (SS). In LTE, the SS has a size dependingon PDCCH format. A UE-specific search space (USS) and a common searchspace (CSS) are separately defined. The USS is set per UE and the rangeof the CSS is signaled to all UEs. The USS and the CSS may overlap for agiven UE. In the case of a considerably small SS with respect to aspecific UE, when some CCEs positions are allocated in the SS, remainingCCEs are not present. Accordingly, the BS may not find CCE resources onwhich PDCCHs will be transmitted to available UEs within givensubframes. To minimize the possibility that this blocking continues tothe next subframe, a UE-specific hopping sequence is applied to thestarting point of the USS.

Table 3 shows sizes of the CSS and USS.

TABLE 3 Number of Number of candidates candidates PDCCH Number of incommon in dedicated format CCEs (n) search space search space 0 1 — 6 12 — 6 2 4 4 2 3 8 2 2

To control computational load of blind decoding based on the number ofblind decoding processes to an appropriate level, the UE is not requiredto simultaneously search for all defined DCI formats. In general, the UEsearches for formats 0 and 1A at all times in the USS. Formats 0 and 1Ahave the same size and are discriminated from each other by a flag in amessage. The UE may need to receive an additional format (e.g. format 1,1B or 2 according to PDSCH transmission mode set by a BS). The UEsearches for formats 1A and 1C in the CSS. Furthermore, the UE may beset to search for format 3 or 3A. Formats 3 and 3A have the same size asthat of formats 0 and 1A and may be discriminated from each other byscrambling CRC with different (common) identifiers rather than aUE-specific identifier. PDSCH transmission schemes and informationcontent of DCI formats according to transmission mode (TM) are arrangedbelow.

Transmission Mode (TM)

-   -   Transmission mode 1: Transmission from a single base station        antenna port    -   Transmission mode 2: Transmit diversity    -   Transmission mode 3: Open-loop spatial multiplexing    -   Transmission mode 4: Closed-loop spatial multiplexing    -   Transmission mode 5: Multi-user MIMO (Multiple Input Multiple        Output)    -   Transmission mode 6: Closed-loop rank-1 precoding    -   Transmission mode 7: Single-antenna port (port5) transmission    -   Transmission mode 8: Double layer transmission (ports 7 and 8)        or single-antenna port (port 7 or 8) transmission    -   Transmission mode 9: Transmission through up to 8 layers (ports        7 to 14) or single-antenna port (port 7 or 8) transmission

DCI Format

-   -   Format 0: Resource grants for PUSCH transmission    -   Format 1: Resource assignments for single codeword PDSCH        transmission (transmission modes 1, 2 and 7)    -   Format 1A: Compact signaling of resource assignments for single        codeword PDSCH (all modes)    -   Format 1B: Compact resource assignments for PDSCH using rank-1        closed loop precoding (mod 6)    -   Format 1C: Very compact resource assignments for PDSCH (e.g.        paging/broadcast system information)    -   Format 1D: Compact resource assignments for PDSCH using        multi-user MIMO (mode 5)    -   Format 2: Resource assignments for PDSCH for closed-loop MIMO        operation (mode 4)    -   Format 2A: Resource assignments for PDSCH for open-loop MIMO        operation (mode 3)    -   Format 3/3A: Power control commands for PUCCH and PUSCH with        2-bit/i-bit power adjustments

FIG. 5 illustrates a structure of an uplink subframe used in LTE(-A).

Referring to FIG. 5, a subframe 500 is composed of two 0.5 ms slots 501.Assuming a length of a normal cyclic prefix (CP), each slot is composedof 7 symbols 502 and one symbol corresponds to one SC-FDMA symbol. Aresource block (RB) 503 is a resource allocation unit corresponding to12 subcarriers in the frequency domain and one slot in the time domain.The structure of the uplink subframe of LTE(-A) is largely divided intoa data region 504 and a control region 505. A data region refers to acommunication resource used for transmission of data such as voice, apacket, etc. transmitted to each UE and includes a physical uplinkshared channel (PUSCH). A control region refers to a communicationresource for transmission of an uplink control signal, for example,downlink channel quality report from each UE, reception ACK/NACK for adownlink signal, uplink scheduling request, etc. and includes a physicaluplink control channel (PUCCH). A sounding reference signal (SRS) istransmitted through an SC-FDMA symbol that is lastly positioned in thetime axis in one subframe. SRSs of a plurality of UEs, which aretransmitted to the last SC-FDMAs of the same subframe, can bedifferentiated according to frequency positions/sequences. The SRS isused to transmit an uplink channel state to an eNB and is periodicallytransmitted according to a subframe period/offset set by a higher layer(e.g., RRC layer) or aperiodically transmitted at the request of theeNB.

In next-generation RAT (Radio Access Technology), a self-containedsubframe is considered in order to minimize data transmission latency.FIG. 6 illustrates a self-contained subframe structure. In FIG. 15, ahatched region represents a DL control region and a black regionrepresents a UL control region. A blank region may be used for DL datatransmission or UL data transmission. DL transmission and ULtransmission are sequentially performed in a single subframe, and thusDL data can be transmitted and UL ACK/NACK can also be received in asubframe. Consequently, a time taken until data retransmission isperformed when a data transmission error is generated is reduced andthus final data delivery latency can be minimized.

As examples of self-contained subframe types which can beconfigured/set, the following four subframe types can be considered.Respective periods are arranged in a time sequence.

-   -   DL control period+DL data period+GP (Guard Period)+UL control        period    -   DL control period+DL data period    -   DL control period+GP+UL data period+UL control period    -   DL control period+GP+UL data period

A PDFICH, a PHICH and a PDCCH can be transmitted in the data controlperiod and a PDSCH can be transmitted in the DL data period. A PUCCH canbe transmitted in the UL control period and a PUSCH can be transmittedin the UL data period. The GP provides a time gap in a process in whicha BS and a UE switch from a transmission mode to a reception mode or ina process in which the BS and the UE switch from the reception mode tothe transmission mode. Some OFDM symbols in a subframe at a time when DLswitches to UL may be set to the GP.

In 3GPP New RAT (NR) system environment, it may be able to differentlyconfigure OFDM numerology (e.g., subcarrier spacing and OFDM symbolduration based on the subcarrier spacing) among a plurality of cellscarrier aggregated on a signal UE. Hence, (absolute time) duration of atime resource configured by the same number of symbols (e.g., an SF, aslot, or a TTI (for clarity, commonly referred to as TU (Time Unit)) canbe differently configured between CA cells. In this case, a symbol caninclude an OFDM symbol and an SC-FDMA symbol.

FIG. 7 illustrates a frame structure defined in 3GPP NR. Similar to aradio frame structure of LTE/LTE-A (refer to FIG. 2), in 3GPP NR, aradio frame includes 10 subframes and each of the subframes has a lengthof 1 ms. A subframe includes one or more slots and a slot length variesdepending on an SCS. 3GPP NR supports SCS of 15 KHz, 30 KHz, 60 KHz, 120KHz, and 240 KHz. In this case, a slot corresponds to a TTI shown inFIG. 6.

Table 4 illustrates a case that the number of symbols per slot, thenumber of slots per frame, and the number of slots per subframe varyaccording to an SCS.

TABLE 4 Number of Number of Number of symbols within slot within slotwithin SCS (15*2{circumflex over ( )}u) slot frame subframe  15 KHz (u =0) 14 10 1  30 KHz (u = 1) 14 20 2  60 KHz (u = 2) 14 40 4 120 KHz (u =3) 14 80 8 240 KHz (u = 4) 14 160 16

Hereinafter, narrowband Internet of Things (NB-IoT) will be described.For convenience, although a description will focus on NB-IoT based onthe 3GPP LTE standard, the following description may be equally appliedeven to the 3GPP NR standard. To this end, modification may be made tointerpretation of some technical configurations (e.g., LTE band→NR bandand subframe→slot).

NB-IoT supports three operation modes: in-band, guard-band, andstand-alone and the same requirements may be applied to each mode.

(1) In-band mode: allocate some of resources in an LTE band to NB-IoT.

(2) Guard-band mode: uses a guard frequency band of LTE and an NB-IoTcarrier is deployed as closely as possible to an edge subcarrier of LTE.

(3) Stand-alone mode: allocate some carriers in a GSM band to NB-IoT.

An NB-IoT UE searches for an anchor carrier in a 100-kHz unit forinitial synchronization and a center frequency of an anchor carrier inthe in-band and the guard-band should be located within ±7.5 kHz from achannel raster of 100 kHz. In addition, 6 physical resource blocks(PRBs) among LTE PRBs are not assigned to NB-IoT. Therefore, the anchorcarrier may be located only in a specific PRB.

FIG. 8 illustrates deployment of an in-band anchor carrier in an LTEbandwidth of 10 MHz.

Referring to FIG. 8, a direct current (DC) subcarrier is located in achannel raster. Since a center frequency spacing between adjacent PRBsis 180 kHz, center frequencies of PRB indexes 4, 9, 14, 19, 30, 35, 40,and 45 are located at ±2.5 kHz from the channel raster. Similarly, acenter frequency of a PRB suitable as an anchor carrier at an LTEbandwidth of 20 MHz is located at ±2.5 kHz from the channel raster andcenter frequencies of PRBs suitable as anchor carriers at LTE bandwidthsof 3 MHz, 5 MHz, and 15 MHz are located at ±7.5 kHz from channel raster.

In the guard-band mode, a center frequency of a PRB immediately adjacentto an edge PRB of LTE at bandwidths of 10 MHz and 20 MHz is located at±2.5 kHz from the channel raster. For bandwidths of 3 MHz, 5 MHz and 15MHz, guard frequency bands corresponding to 3 subcarriers from the edgePRB may be used to position a center frequency of an anchor carrier at±7.5 kHz from the channel raster.

The anchor carrier in the stand-alone mode is arranged at a channelraster of 100 kHz and all GSM carriers, including a DC carrier, may beused as NB-IoT anchor carriers.

NB-IoT supports multiple carriers and a combination of in-band+in-band,in-band+guard-band, guard band+guard-band, or stand-alone+stand-alonemay be used.

NB-IoT DL uses an OFDMA scheme having a subcarrier spacing of 15 kHz.This provides orthogonality between subcarriers to facilitatecoexistence with an LTE system.

NB-IoT DL is provided with physical channels such as a narrowbandphysical broadcast channel (NPBCH), a narrowband physical downlinkshared channel (NPDSCH), and a narrowband physical downlink controlchannel (NPDCCH) and is provided with physical signals such as anarrowband primary synchronization signal (NPSS), a narrowband primarysynchronization signal (NSSS), and a narrowband reference signal (NRS).

The NPBCH delivers a master information block-narrowband (MIB-NB), whichis minimum system information necessary for the NB-IoT UE to access asystem, to the UE. An NPBCH signal may be transmitted a total of 8 timesto improve coverage. A transport block size (TBS) of the MIB-NB is 34bits and is newly updated at a TTI period of every 640 ms. The MIB-NBincludes information such as an operation mode, a system frame number(SFN), a hyper-SFN, the number of cell-specific reference signal (CRS)ports, a channel raster offset, etc.

The NPSS consists of a Zadoff-Chu (ZC) sequence having a length of 11and a root index of 5. The NPSS may be generated according to thefollowing equation.

$\begin{matrix}{{{d_{l}(n)} = {{S(l)} \cdot e^{{- j}\frac{\pi\;{{un}{({n + 1})}}}{11}}}},{n = 0},1,\ldots\;,10} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

Here, S(l) for an OFDM symbol index l may be defined as shown in Table5.

TABLE 5 Cyclic prefix length S(3), . . . , S(13) Normal 1 1 1 1 −1 −1 11 1 −1 1

The NSSS consists of a combination of a ZC sequence having a length of131 and a binary scrambling sequence such as a Hadamard sequence. TheNSSS indicates a physical cell ID (PCID) through the combination of theabove sequences to NB-IoT UEs in a cell.

The NSSS may be generated according to the following equation.

$\begin{matrix}{{d(n)} = {{b_{q}(m)}e^{{- j}\; 2{\pi\theta}_{f}n}e^{{- j}\frac{\pi\;{{un}^{\prime}{({n^{\prime} + 1})}}}{131}}}} & \left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack\end{matrix}$

Here, variables applied to Equation 2 may be defined as follows.

$\begin{matrix}{{{n = 0},1,\ldots\;,131}{n^{\prime} = {n\mspace{14mu}{mod}\; 131}}{m = {n\mspace{14mu}{mod}\; 128}}{u = {{N_{ID}^{Ncell}{mod}\; 126} + 3}}{q = \left\lfloor \frac{N_{ID}^{Ncell}}{126} \right\rfloor}} & \left\lbrack {{Equation}\mspace{14mu} 3} \right\rbrack\end{matrix}$

Here, a binary sequence b_(q) (m) is defined as shown in Table 6 andb₀(m) to b₃(m) correspond to columns 1, 32, 64, and 128 of a Hadamardmatrix of order 128, respectively. A cyclic shift θ_(f) for a framenumber n_(f) may be defined as indicated in Equation 4.

TABLE 6 q b_(q)(0), . . . b_(q)(127) 0 [1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 11 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 11 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 11 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 11 1 1 1] 1 [1 −1 −1 1 −1 1 1 −1 −1 1 1 −1 1 −1 −1 1 −1 1 1 −1 1 −1 −1 11 −1 −1 1 −1 1 1 −1 1 −1 −1 1 −1 1 1 −1 −1 1 1 −1 1 −1 −1 1 −1 1 1 −1 1−1 −1 1 1 −1 −1 1 −1 1 1 −1 1 −1 −1 1 −1 1 1 −1 −1 1 1 −1 1 −1 −1 1 −1 11 −1 1 −1 −1 1 1 −1 −1 1 −1 1 1 −1 1 −1 −1 1 −1 1 1 −1 −1 1 1 −1 1 −1 −11 −1 1 1 −1 1 −1 −1 1 1 −1 −1 1 −1 1 1 −1 ] 2 [1 −1 −1 1 −1 1 1 −1 −1 11 −1 1 −1 −1 1 −1 1 1 −1 1 −1 −1 1 1 −1 −1 1 −1 1 1 −1 −1 1 1 −1 1 −1 −11 1 −1 −1 1 −1 1 1 −1 1 −1 −1 1 −1 1 1 −1 −1 1 1 −1 1 −1 −1 1 1 −1 −1 1−1 1 1 −1 −1 1 1 −1 1 −1 −1 1 −1 1 1 −1 1 −1 −1 1 1 −1 −1 1 −1 1 1 −1 −11 1 −1 1 −1 −1 1 1 −1 −1 1 −1 1 1 −1 1 −1 −1 1 −1 1 1 −1 −1 1 1 −1 1 −1−1 1] 3 [1 −1 −1 1 −1 1 1 −1 −1 1 1 −1 1 −1 −1 1 −1 1 1 −1 1 −1 −1 1 1−1 −1 1 −1 1 1 −1 −1 1 1 −1 1 −1 −1 1 1 −1 −1 1 −1 1 1 −1 1 −1 −1 1 −1 11 −1 −1 1 1 −1 1 −1 −1 1 −1 1 1 −1 1 −1 −1 1 1 −1 −1 1 −1 1 1 −1 1 −1 −11 −1 1 1 −1 −1 1 1 −1 1 −1 −1 1 1 −1 −1 1 −1 1 1 −1 −1 1 1 −1 1 −1 −1 1−1 1 1 −1 1 −1 −1 1 1 −1 −1 1 −1 1 1 −1]

$\begin{matrix}{\theta_{f} = {\frac{33}{132}\left( {n_{f}\text{/}2} \right){mod}\; 4}} & \left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack\end{matrix}$

Here, n_(f) denotes a radio frame number and mod denotes a modulofunction.

The NRS is provided as a reference signal for channel estimationrequired for DL physical channel demodulation and is generated in thesame manner as in LTE. However, a narrowband-physical cell ID (NB-PCID)(or an NCell ID or an NB-IoT BS ID) is used as an initial value forinitialization. The NRS is transmitted through one or two antenna ports(p=2000 or 2001).

The NPDCCH has the same transmit antenna configuration as the NPBCH andcarries DCI. The NPDCCH supports three DCI formats. DCI format N0includes narrowband physical uplink shared channel (NPUSCH) schedulinginformation and DCI formats N1 and N2 include NPDSCH schedulinginformation. The NPDCCH may perform a maximum of 2048 repetitivetransmissions to improve coverage.

The NPDSCH is used to transmit data (e.g., transport block (TB)) of atransport channel such as a DL-shared channel (DL-SCH) and a pagingchannel (PCH). A maximum TBS is 680 bits and the NPDSCH may perform amaximum of 2048 repetitive transmissions to improve coverage.

FIG. 9 illustrates locations at which NB-IoT DL physicalchannels/signals are transmitted in an FDD LTE system.

Referring to FIG. 9, an NPBCH is transmitted in the first subframe ofevery frame, an NPSS is the sixth subframe of every frame, and an NSSSis transmitted in the last (e.g., 10th) subframe of every even frame. AnNB-IoT UE acquires frequency, symbol, and frame synchronization usingsynchronization signals (NPSS and NSSS) and searches for 504 physicalcell IDs (i.e., BS IDs). An LTE synchronization signal is transmittedthrough 6 PRBs and an NB-IoT synchronization signal is transmittedthrough one PRB.

In NB-IoT, a UL physical channel consists of a narrowband physicalrandom access channel (NPRACH) and an NPUSCH and supports single-tonetransmission and multi-tone transmission. Single-tone transmission issupported for subcarrier spacings of 3.5 kHz and 15 kHz and multi-tonetransmission is supported only for a subcarrier spacing of 15 kHz. OnUL, the subcarrier spacing of 15 kHz may maintain orthogonality with LTEto provide optimal performance, whereas the subcarrier spacing of 3.75kHz may lower orthogonality so that performance deterioration may occurdue to interference.

An NPRACH preamble consists of 4 symbol groups and each symbol groupconsists of a CP and 5 (SC-FDMA) symbols. The NPRACH supports onlysingle-tone transmission with a subcarrier spacing of 3.75 kHz andprovides CPs of lengths of 66.7 μs and 266.67 μs to support differentcell radii. Each symbol group performs frequency hopping and a hoppingpattern thereof is as follows. A subcarrier transmitting the firstsymbol group is determined in a pseudo-random manner. The second symbolgroup performs 1-subcarrier hopping, the third symbol group performs6-subcarrier hopping, and the fourth symbol group performs 1-subcarrierhopping. In the case of repetitive transmission, a frequency hoppingprocedure is repeatedly applied and the NPRACH preamble may berepeatedly transmitted up to 128 times to improve coverage.

The NPUSCH supports two formats. NPUSCH format 1 is used for UL-SCHtransmission and a maximum TBS is 1000 bits. NPUSCH format 2 is used forUL control information transmission such as HARQ ACK signaling. NPUSCHformat 1 supports single-/multi-tone transmission and NPUSCH format 2supports only single-tone transmission. In the case of single-tonetransmission, pi/2-binary phase shift keying (BPSK) and pi/4-quadraturephase shift keying (QPSK) are used to reduce a peak-to-average powerratio (PAPR).

In the stand-alone and guard-band modes, all resources included in onePRB may be allocated to NB-IoT. However, in the case of the in-bandmode, resource mapping is restricted for coexistence with a legacy LTEsignal. For example, in the in-band mode, resources classified as an LTEcontrol channel allocation area (OFDM symbols 0 to 2 of every subframe)may not be allocated to the NPSS/NSSS and an NPSS/NSSS symbol mapped toan LTE CRS RE is punctured.

FIG. 10 illustrates resource allocation of an NB-IoT signal and an LTEsignal in an in-band mode. Referring to FIG. 10, for ease ofimplementation, an NPSS and an NSSS are not transmitted in OFDM symbolscorresponding to a control region of an LTE system (e.g., the firstthree OFDM symbols in a subframe) regardless of an operation mode. Inaddition, an NPSS/NSS RE colliding with an LTE CRS RE on a physicalresource is punctured and mapped so as not to affect the LTE system.

After cell search, the NB-IoT UE demodulates an NPBCH in a situation inwhich system information other than a PCID is absent. Therefore, anNPBCH symbol may not be mapped to the LTE control channel allocationregion. In the absence of the system information, since the NB-IoT UEassumes 4 LTE antenna ports (e.g., p=0, 1, 2, and 3) and two NB-IoTantenna ports (e.g., p=2000 and 2001), the NPBCH may not be allocated toan CRS RE and an NRS RE. Therefore, the NPBCH is rate-matched to givenavailable resources.

After NPBCH demodulation, the NB-IoT UE obtains information about thenumber of CRS antenna ports. However, the NB-IoT UE is not still awareof information about the LTE control channel allocation region.Accordingly, the NPDSCH that transmits system information block type 1(SIB1) data is not mapped to a resource classified as the LTE controlchannel allocation region.

However, unlike the NPBCH, an RE that is not actually allocated to anLTE CRS may be allocated to the NPDSCH. After receiving SIB1, since theNB-IoT UE acquires all information related to resource mapping, a BS maymap the NPDSCH (except when transmitting SIB1) and the NPDCCH toavailable resources based on LTE control channel information and thenumber of CRS antenna ports.

Embodiment: Inter-Cell Interference Mitigation for NB-IoT

The present disclosure proposes an adaptive scrambling method capable ofrandomizing inter-cell interference while minimizing receptioncomplexity of a UE in an NB-IoT system. The scrambling method of thepresent disclosure may be used for, but is not limited to, an NPDCCH andan NPDSCH. The present disclosure also proposes a (transmission)symbol-level scrambling and interleaving method for inter-cellinterference randomization without greatly increasing complexity of anNB-IoT UE. The proposed methods are not limited to the NB-IoT system andare applicable to any system that allows many repetitive transmissionsfor a low-power, low-cost UE such as enhanced machine-type communication(eMTC).

1. Reception Complexity and DL Repetitive Transmission of UE

Scrambling of an NPDSCH carrying BCCH (data) is initialized in asubframe in which the NPDSCH is first transmitted and then reinitializedby differing in a slot number in every fourth NPDSCH subframe. Inaddition, scrambling of an NPDSCH not carrying the BCCH (data) isinitialized in a subframe in which a codeword is first transmitted andthen reinitialized by differing in a radio frame and a slot numberwhenever every min(M^(PDCCH) _(rep), 4)-th repetitive transmission ofthe codeword is performed. Scrambling initialization of the NPDSCH notcarrying the BCCH (data) may be represented as illustrated in FIG. 11according to N_(SF) and N_(Rep) where N_(SF) denotes the number ofsubframes in which the codeword is transmitted and N_(Rep) denotes therepetitive number of subframes and is equal to M^(PDCCH) _(rep). In thefigure, n_(RNTI) denotes a UE ID (e.g., C-RNRI), n_(f) denotes a radioframe number, n_(s) denotes the first slot number used for repetitivetransmission in a radio frame, and N^(Ncell) _(ID) denotes an NCell ID(NB-IoT BS ID).

Unlike a method of initializing scrambling in every subframe in a legacyLTE system, the reason why scrambling initialization of the NPDSCH notcarrying the BCCH (data) is applied as illustrated in FIG. 11 is thatone codeword is repeatedly transmitted in multiple subframes in theNB-IoT system unlike the legacy LTE system. In this case, if scramblingis initialized in every subframe in the same method as in the legacy LTEsystem, reception complexity of the UE may be greatly increased. In FIG.11, for example, when N_(Rep) is 8, if scrambling is initialized everytime during a duration of ‘A’ in which repetitive transmission isperformed in four subframes, the UE needs to combine ‘A’ of four timeswhich is repeatedly transmitted by demodulating every subframe. On theother hand, if scrambling is maintained during four subframes, the UEmay add all ‘A’ repeatedly transmitted four times in the time domain,and then perform fast Fourier transformation (FFT) of one time anddemodulation. In particular, since reduction of operation complexity isa very important factor for a low-power mode UE such as an NB-IoT UE, ascrambling initialization method different from that used in the legacyLTE system is used.

2. Enhanced Scrambling for Inter-Cell Interference Randomization

As described above, although the scrambling initialization method of theNB-IoT system is efficient in terms of UE complexity, the method is noteffective as a method of mitigating interference between adjacent cells.In this regard, there has been a recent demand that scrambling methodsof an NPDCCH and an NPDSCH should be improved and modifications to thescrambling methods based on 3GPP Rel-14 NB-IoT are expected to be made.Prior to this, a scrambling method of an NPBCH has already been revisedfor a similar reason and initialization methods of the NPDCCH and theNPDSCH are also expected to be modified similarly to an initializationmethod of the NPBCH. However, since effects of the scramblingmodification of the NPDCCH and NPDSCH on reception complexity of the UEmay be completely different from that of the NPBCH, a more carefulmodification is required. Before description of this modification, anNPBCH scrambling method revised in 3GPP Rel-13 will be described first.

Table 7 shows a conventional NPBCH repetitive transmission method andTable 8 shows a modified NPBCH repetitive transmission method.

TABLE 7 Conventional method 1) Get a block of complex-valued symbols(=modulation symbols) y^(p) (N), ..., y^(p) (N + K − 1) N = startingindex for the 80ms block (N = 0, 100, ..., 700) K = number of symbols in1 subframe (K = 100) 2) Repeat the same block in 8 consecutive NPBCHsubframes

TABLE 8 • Modified method 1) Get a block of complex-valued symbols(=modulation symbols) y^(p)(N), ... , y^(p) (N + K − 1)  N = startingindex for the 80ms block (N = 0, 100, ..., 700)  K = number of symbolsin 1 subframe (K = 100) 2) For each of the 8 consecutive NPBCH subframes(indices j=0,...,7), the block of K symbols to be transmitted isobtained as follows      y_(j) ^(p)(i) = y^(p)(i)θ_(j)(i) Where θ(i)isobtained as      ${\theta_{j}(i)} = \left\{ \begin{matrix}{{1\mspace{14mu}{if}\mspace{14mu}{c_{j}\left( {2i} \right)}} = {{0\mspace{14mu}{and}\mspace{14mu}{c_{j}\left( {{2i} + 1} \right)}} = 0}} \\{{{- 1}\mspace{14mu}{if}\mspace{14mu}{c_{j}\left( {2i} \right)}} = {{0\mspace{14mu}{and}\mspace{14mu}{c_{j}\left( {{2i} + 1} \right)}} = 1}} \\{{j\mspace{14mu}{if}\mspace{14mu}{c_{j}\left( {2i} \right)}} = {{1\mspace{14mu}{and}\mspace{14mu}{c_{j}\left( {{2i} + 1} \right)}} = 0}} \\{{{- j}\mspace{14mu}{if}\mspace{14mu}{c_{j}\left( {2i} \right)}} = {{1\mspace{14mu}{and}\mspace{14mu}{c_{j}\left( {{2i} + 1} \right)}} = 1}}\end{matrix} \right.$ And c_(j)(i) is a scrambling sequence initializedby c_(init,j) = N_(ID) ^(Ncell) + (n_(f)mod8)2⁹ c_(j)(i),i = 0, ... ,199is given by    c(n) = (x₁(n + N_(C)) + x₂(n + N_(C)))mod2   x₁(n + 31) =(x₁(n + 3) + x₁(n))mod2   x₂(n + 31) = (x₂(n + 3) + x₂(n + 2) +x₂(n + 1) + x₂(n))mod2 where N_(C) = 1600 and the first m-sequence shallbe initialized with x₁(0) = 1,x₁(n) = 0,n = 1,2,...,30. Theinitialization of the second m-sequence is denotted by c_(init) =Σ_(i=0) ³⁰ x₂(i)·2^(i).

FIG. 12 illustrates an NPBCH transmission method. Referring to FIG. 12,a scrambling sequence applied to an NPBCH is initialized with a value ofan N^(Ncell) _(ID) every 640 ms. In addition, the NPBCH carries 1600coded bits for 640 ms and different information blocks A to H transmitbits every 80 ms. Each information block is repeated at intervals of 10ms within 80 ms. Specifically, the NPBCH is transmitted in the firstsubframe (e.g., subframe 0) of a radio frame. Quadrature phase shiftkeying (QPSK) is applied to the NPBCH. 100 complex-symbols (i.e.,modulation symbols) are mapped to each subframe.

According to the conventional method of Table 7, the same signal istransmitted every 10 ms within 80 ms (e.g., subframes 8n to 8n+7 wheren=0 to 7). Since the NPBCH is always transmitted in the first subframeof a radio frame, the same signal is transmitted even in an RE in whichan NRS and a CRS are transmitted.

On the other hand, according to the modified method of Table 8, adifferent scrambling sequence is additionally applied every 10 ms within80 ms (e.g., subframes 8n to 8n+7 where n=0 to 7). Here, a scramblingsequence applied for 80 ms may have a complex value as opposed to theconventional method and has a feature that the scrambling sequence isnot repeated every 10 ms for 80 ms during which ‘A’ of FIG. 12 istransmitted. Therefore, before combining a signal transmitted 8 timesfor 80 ms, a receiver needs to perform descrambling first. Here, since adescrambling operation is a procedure of simply removing a complex valueof 1, −1, j, or −j, it may be assumed that no additional complexity isincreased. However, in order to perform descrambling of each RE in thefrequency domain, it is necessary to perform FFT for each OFDM symbolwithin 80 ms. Therefore, there may be a disadvantage in that the numberof FFT operations of the UE increases as compared with conventionalperfect repetitive transmission within 80 ms. However, since 10 ms isnot sufficiently short considering a coherence time, it is difficult tocombine each OFDM symbol repeated in units of 10 ms within 80 ms beforeperforming FFT for each OFDM symbol even when the conventionalscrambling method is performed. For this reason, the modified NPBCHscrambling method may be implemented without additionally increasingcomplexity of the UE receiver.

An inter-cell interference effect may similarly appear in not only theNPBCH but also in the repeatedly transmitted NPDCCH and NPDSCH.Therefore, almost the same method as the modified NPBCH scramblingmethod of Table 8 is proposed even for the NPDCCH and the NPDSCH.However, unlike the NPBCH repeated every 10 ms, the NPDCCH and theNPDSCH may be repeatedly transmitted at a period of 1 ms in a DL validsubframe indicated by ‘1’ in DL-bitmap-NB. Here, the valid subframeindicates a subframe in which the NRS is transmitted and the NPDCCH andNPDSCH may be transmitted. Therefore, when different scramblingsequences are applied to subframes in which the NPDCCH and the NPDSCHare repeatedly transmitted, reception complexity of the UE may begreatly affected unlike the NPBCH. That is, prior to combining theNPDCCH/NPDSCH repeatedly transmitted within a duration shorter than thecoherence time, an additional FFT operation may be required.

Tables 9 to 11 show the number of FFT operations of the NPDSCH when adifferent scrambling sequence is applied to each subframe similarly tothe modified NPBCH scrambling method of Table 8. Tables 9 to 11 show anin-band same PCI mode, an in-band different PCI mode, and otheroperation modes, respectively.

TABLE 9 CFI = 1 CFI = 2 CFI = 3 Existing Change Increase Existing ChangeIncrease Existing Change Increase M = 1 14 14  0% 13 13  0% 12 12  0% M= 2 22 28 27% 21 26 24% 20 24 20% M = 4 38 56 47% 37 52 41% 36 48 33%

TABLE 10 CFI = 1 CFI = 2 CFI = 3 Existing Change Increase ExistingChange Increase Existing Change Increase M = 1 13 13  0% 12 12  0% 11 11 0% M = 2 17 26 53% 16 24 50% 15 22 47% M = 4 25 52 108%  24 48 100%  2344 91%

TABLE 11 CFI = 0 (No control region) Existing Change Increase M = 1 1414  0% M = 2 18 28 56% M = 4 26 56 115% 

Here, M represents the number of repetitions of NPDSCH transmission.When the conventional NPDSCH scrambling method is applied, the samescrambling sequence is applied during M subframe durations. The numberof FFT operations of the NPDSCH is different from the number of FFToperations of the NPBCH in that an OFDM symbol in which a CRS and an NRSare transmitted requires an FFT operation every time regardless ofwhether combining is performed because different signals may betransmitted in M subframe durations in which the CRS and the NRS maytransmitted. However, there is a difference in that the CRS is not usedin the in-band different PCI mode and a control region is not present inthe other operation modes. As may be confirmed from Tables 9 to 11, asthe number M of repetitive transmissions increases, complexity greatlyincreases when the modified NPBCH scrambling method is applied to theNPDSCH relative to the conventional scrambling method.

3. Adaptive Scrambling for NPDCCH and NPDSCH

As described above, the inter-cell interference randomization scramblingmethod of the NPBCH (see Table 8) is not suitable for the NPDCCH andNPDSCH in terms of complexity of the UE receiver. In particular, for aUE-specific channel, it is necessary to apply inter-cell interferencerandomization scrambling more carefully. Accordingly, the presentdisclosure proposes a method of effectively applying a scrambling methodfor inter-cell interference randomization applied to the NPDCCH and/orthe NPDSCH. The proposed method relates to a method of more adaptivelyapplying inter-cell interference randomization scrambling applied to theNPDCCH and/or the NPDSCH according to a radio environment of each UE.The core of the proposed method is not to apply scrambling forinter-cell interference randomization applied to the NPDCCH and/or theNPDSCH to a UE that is not in an interference limited environment. Thatis, scrambling for inter-cell interference randomization applied to theNPDCCH and/or the NPDSCH may be selectively/adaptively applied only to aUE that is in the interference limited environment.

Various specific methods for this purpose will be described below. Forconvenience, in the following description, inter-cell interferencerandomization scrambling means inter-cell interference randomizationscrambling applied to the NPDCCH and/or the NPDSCH, unless otherwisespecified.

First, inter-cell interference randomization scrambling is needed whenthe UE receives signals of high power from an inter-cell. However, evenin this case, when the inter-cell signals are operated asynchronouslywith a serving cell or when the difference between arrival times of theinter-cell received signals is larger than a predetermined value, it isdifficult to expect an inter-cell interference randomization effectthrough scrambling. In addition, even when power of the signals receivedfrom the inter-cell is high, if power of a signal received from theserving cell is higher or a main reason for performance degradation ofthe receiver is noise rather than interference, it is difficult toexpect performance improvement caused by inter-cell interferencerandomization scrambling. In addition, even if power of an NRS receivedfrom the inter-cell is high, when there is less NPDCCH and NPDSCHscheduling, a demand for inter-cell interference randomization may bereduced.

[Method #1 (Semi-)Static Method]

A BS may enable or disable inter-cell interference randomizationscrambling based on a higher layer signal (e.g., RRC). Anenabled/disabled condition may be cell-common or UE-specific. Inaddition, inter-cell interference randomization scrambling may beenabled/disabled only for a specific physical channel. For example,inter-cell interference scrambling may be disabled only for an NPCCHincluded in a USS and may be enabled for an NPCCH included in a CSS. Inaddition, inter-cell interference scrambling of the NPDCCH may bedisabled only for a specific RNTI type. In addition, inter-cellinterference scrambling may be disabled for an NPDSCH scheduled by anNPDCCH having the specific RNTI type. Inter-cell interference scramblingmay also be disabled or enabled independently for the NPDCCH and theNPDSCH. For example, inter-cell interference scrambling is disabled forthe NPDCCH, whereas whether inter-cell interference scrambling of theNPDCH is enabled/disabled may be explicitly indicated through the NPDCCH(DL grant) that schedules the NPDSCH. Generally, it may be desirable toenable inter-cell interference scrambling for the NPDCCH and/or theNPDSCH, which need to be decoded by all users, not by a particular user.Additionally, unlike an NPDSCH scheduled based on the DL grant, otherNPDSCHs (e.g., SIB1-NB and other SIB messages) may always be enabled ordisabled or may be enabled or disabled only when a certain condition issatisfied. For example, when an MIB-NB indicates a value lower than aspecific value as the number of repetitions of SIB1-NB and/or a TBS ofthe SIB1-NB, inter-cell interference scrambling may be defined to bedisabled. Conditions for (semi-)statically enabling/disabling inter-cellinterference scrambling include an RNTI type, an NPDCCH type (CSS orUSS), the maximum number of repetitions of the NPDCCH, an NPDCCHaggregation level, a coverage extension (CE) level, number ofrepetitions of the NPDSCH, an NPDSCH MCS, an NPDSCH TBS, an NPDSCH coderate, etc., which may be applied together in a non-exclusive manner. Forexample, when the BS operates CE levels 0, 1, and 2, the NPDSCH higherthan a specific code rate (a TBS, an MCS, or the number of repetitionsof the NPDSCH) may be scheduled for a UE belonging to CE level 0. Inthis case, since an SINR situation of the UE may be regarded as good,inter-cell interference scrambling of the NPDCCH and/or the NPDSCH maybe disabled.

There may be a situation in which inter-cell interference scrambling mayalways be enabled, for example, when the number of consecutive DLsubframes in TDD is not sufficient. An advantage obtained wheninter-cell interference scrambling is disabled is to minimize additionalincrease in complexity of the UE. However, when the number ofconsecutive DL subframes is not sufficient, since OFDM symbol-levelcombining may not be effectively applied, inter-cell interferencescrambling may always be enabled according to a duplex mode and/or TDDUL/DL configuration. For the same reason, inter-cell interferencescrambling may always be enabled even in FDD according to DL validsubframe configuration. In addition, even in TDD and FDD, inter-cellinterference scrambling may be enabled or disabled for the NPDCCH andthe NPDSCH by further considering other conditions (e.g., the number ofrepetitive transmissions).

In contrast, there may be a situation in which inter-cell interferencescrambling may always be disabled. For example, when cell operationbetween adjacent BSs is asynchronous, inter-cell interference scramblingmay not help to improve reception performance of the UE. As anotherexample, in an environment in which adjacent BSs operate networks usingdifferent carriers or in an isolated cell environment, inter-cellinterference scrambling may always be disabled.

Enabling/disabling inter-cell interference scrambling may be appliedindependently to an anchor carrier and a non-anchor carrier. Forexample, the anchor carrier may have high inter-cell interference,whereas there may be an environment in which inter-cell interferencescrambling may be disabled for the non-anchor carrier by allocatingdifferent PRBs between cells. That is, the mentionedconditions/parameters that may enable/disable inter-cell interferencescrambling may be applied differently/independently with respect to theanchor carrier and the non-anchor carrier. In addition, the UE mayreceive a new parameter set and condition related to inter-cellinterference scrambling for the non-anchor carrier in the process ofconfiguring the non-anchor carrier.

[Method #2 Dynamic Method]

Inter-cell interference scrambling may be enabled or disabled duringevery NPDCCH and/or NPDSCH transmission or inter-cell interferencescrambling may be enabled/disabled in a specific period unit. Here,dynamically enabling/disabling inter-cell interference scrambling mayinclude a method of enabling/disabling inter-cell interferencescrambling according to an NPDCCH and/or NPDSCH condition at a specificmoment based on the (semi-)statically preset parameter set and condition(of Method #1). For example, whether inter-cell interference scramblingis enabled/disabled for a specific RNTI type may be indicated through ahigher layer (e.g., RRC) and inter-cell interference scrambling for theNPDSCH may actually be enabled/disabled through the NPDCCH.

First, as a method of enabling/disabling inter-cell interferencescrambling in a specific period unit, a specific period and duration maybe set through a higher layer (e.g., RRC) and inter-cell interferencescrambling may be enabled/disabled through the NPDCCH, the NPDSCH, orthird signaling (e.g., paging, or a newly added sequence and channel forpower consumption reduction such as paging skipping) in a predeterminedtime duration. To this end, the UE may blind-decode a DCI formatdifferent from a legacy DCI format during the predetermined specifictime duration or interpret the DCI format differently from aconventional interpretation method. In addition, an indication ofenabling/disabling inter-cell interference randomization scrambling maybe included in a sequence for scrambling DCI and in CRC maskinginformation. In addition, the indication of enabling/disablinginter-cell interference randomization scrambling in a correspondingduration may be applied up to the next duration and may be indicated inadvance even when related information is not detected in the nextduration. Further, a predetermined specific duration and period may beupdated or may expire every inter-cell interference scramblingenabling/disabling period. In consideration of missing/false alarm ofthe UE for the indication of enabling/disabling inter-cell interferencescrambling, enabling/disabling inter-cell interference scrambling maynot be indicated under a specific condition or enabling/disablinginter-cell interference scrambling may be reset when the NPDCCH is notdetected for a prescribed time or more (fallback method). Even afterindicating inter-cell interference randomization scrambling, the BS maynot perform or follow the indicated enabling/disabling until a specificduration or condition is satisfied in consideration of missing/falsealarm of the UE.

Together with the above method, inter-cell interference scrambling maybe enabled/disabled during every NPDSCH scheduling, which may beindicated through the NPDCCH that schedules the corresponding NPDSCH. Asdescribed in Method #1, an NPDCCH search space, RNTI type information,etc., to/for which enabling/disabling of adaptive inter-cellinterference scrambling may be applied/supported, may be preset by a(semi-)static method rather than a dynamic method.

[Method #3 UE Request Based Method]

Determination of an environment suitable for applying inter-cellinterference scrambling may be indirectly performed from the viewpointof the BS or whether to apply enabling/disabling of inter-cellinterference scrambling may be directly determined at the request of theUE. Here, the method of indirectly determining whether to applyinter-cell interference scrambling includes parameter combinationsdescribed in Method #1 and Method #2 and may be additionally performedbased on an open-loop link adaptation of the BS. As an example of theopen-loop link adaptation-based method, if ACK for NPDSCH transmissionat a rate higher than a specific code rate is frequently reported fromthe UE in the process of UL/DL scheduling, the BS may indirectlydetermine that the environment has little inter-cell interference. Here,the code rate includes an MCS, a TBS, the number of repetitions of theNPDCCH, etc. and the number of repetitions of the NPDCCH may also be theindirect determination basis. For example, if ACK or NACK is reportedfor an NPDSCH scheduled by an NPDCCH of the number of repetitions and anaggregation level, smaller than a specific value, or if an NPUSCHscheduled by the NPDCCH of the number of repetitions and an aggregationlevel, smaller than a specific value, is received from the UE, the BSmay be indirectly aware that a wireless environment of the UE is not aninter-cell interference limited environment. In a similar manner, thedistance between the BS and the UE may be roughly inferred according toa CE level and a timing advance (TA) value of the UE and, based on this,the BS may be indirectly aware of whether an environment is aninter-cell interference limited environment. Such indirect determinationof whether an environment is an inter-cell interference environment maybe implemented by various methods in the BS in most cases.

On the other hand, there may be a method in which the UE directlyrequests that enabling/disabling inter-cell interference scrambling beapplied. In this case, the BS may use Method #1 and Method #2 as amethod of responding to the inter-cell interference scramblingenabling/disabling request of the UE. Meanwhile, since the BS mayenable/disable inter-cell interference scrambling according to therequest of the UE, the request of the UE may be a report on aninter-cell interference level other than an explicit inter-cellinterference scrambling enabling/disabling request. In the presentdisclosure, the inter-cell interference scrambling enabling/disablingrequest and the report on the inter-cell interference level arecollectively referred to as an inter-cell interference informationreport without distinguishing therebetween.

The inter-cell interference information report may be performed by theUE in an indirect or direct manner with respect to the BS in an NPRACH(msg1) resource selection or msg3 transmission step of a random accessprocedure. Accordingly, the BS may indicate enabling/disabling ofinter-cell interference scrambling through a random access response(RAR, msg2) or msg4. Alternatively, the BS may instruct the UE totransmit an NPDCCH ordered NPRACH. In this process, the UE may reportinter-cell interference information in a similar procedure to the abovemethod and the BS may indicate enabling/disabling of inter-cellinterference randomization scrambling. As another method using therandom access procedure, the UE may additionally inform the BS of theinter-cell interference information report in a buffer status reporting(BSR) or data volume and power headroom reporting procedure.

The UE transmits an ACK/NACK report on the NPDSCH on a resourceindicated by a DL grant. In this case, the UE may multiplex and transmitthe inter-cell interference information report. In addition, a new typeof channel and procedure for the inter-cell interference informationreport, rather than an ACK/NACK report for the NPDSCH, may be defined.For example, a trigger condition of other purposes except for NPDSCHscheduling may be defined as a condition for triggering NPUSCH format 2.The BS may receive the inter-cell interference information report usingNPUSCH format 2. Alternatively, the BS may instruct the UE to transmitNPUSCH format 1 using a UL grant. In this case, a method of indicatingthe contents transmitted in NPUSCH format 1 by the inter-cellinterference information report, rather than user data (e.g., UL-SCHdata), may be newly defined. Alternatively, there may be a method ofindicating the inter-cell interference information report by defining athird format other than NPUSCH formats 1 and 2. An NPDCCH detectionoperation performed by the UE after NPUSCH transmission may be defineddifferently from a conventional method. For example, a procedure may bemodified to expect instruction of the BS based on Method #2.

4. (Transmission) Symbol-Level Scrambling and Interleaving forInter-Cell Interference Randomization

When the method of Table 8 is applied without change for inter-cellinterference randomization of the NPDCCH and/or the NPDSCH, a scramblingsequence is multiplied by all REs (or modulation symbols) throughout anNPDCCH and/or NPDSCH subframe. That is, when the NPDCCH and/or theNPDSCH is repeatedly transmitted during N subframes, scramblingsequences of the number of REs (or modulation symbols) of one subframelength generated in a starting subframe are not repeated during Nsubframes, and different scrambling sequences generated in each subframeare multiplied by an I/Q phase of each RE (or modulation symbol) toallow an inter-cell transmission signal to be maximally randomized at anRE (or modulation symbol) level. This increases operation complexity ofthe NB-IoT UE for inter-cell interference randomization as describedabove. To solve this problem, the present disclosure proposes a methodof randomizing inter-cell interference while minimizing receptioncomplexity of the NB-IoT UE. The proposed method may be used to expectthe same or similar effect not only for an NB-IoT system but also forany system using repetitive transmission in a narrow band and may beapplied to DL, UL, and any link direction such as sidelink. Inparticular, scrambling and interleaving proposed by the presentdisclosure may be similarly applied between repeated symbols even ifthere are some repeated symbols although transmission is not completelyrepeated transmission. In addition, the present disclosure may beapplied to a system in which one or more data are modulated andtransmitted during a specific symbol duration such as single carrier(SC) OFDM (=SC-FDMA) rather than an OFDM-based communication system. Forconvenience of description, the proposed method will be described basedon an OFDM-based NB-IoT DL system.

For description, it is assumed that the system is configured such that NREs (e.g., 12 REs) are present in one transmission symbol in thefrequency domain, data is transmitted in units of subframes eachconsisting of M transmission symbols, and one subframe is repeatedlytransmitted during L subframes, as illustrated in FIG. 13. That is, N*Mdata (or demodulation symbols) are mapped and transmitted in onesubframe, which is repeatedly transmitted L times to improve receptionSNR of the UE. Here, the subframe corresponds to a minimum data bundlerepeatedly transmitted and may be replaced with another term such as aslot. According to configuration/scheduling, one data may be transmittedin P subframes. In this case, data may be transmitted in P*L subframes(or slots). Here, the data may include DCI for the NPDCCH, a TB for theNPDSCH, and the TB or UCI (e.g., ACK/NACK) for the NPUSCH. In addition,it is assumed to easily describe the core of the proposal that referencesignals for demodulation (e.g., an NRS and a DMRS) are not included. TheNPDCCH/NPDSCH may be mapped to 12 subcarriers and the NPUSCH may bemapped to 1, 3, 6, or 12 subcarriers.

[Method #4 Symbol-Level Scrambling]

Symbol-level scrambling proposed is a method of applying primaryscrambling at an RE-level during a specific time duration and thenapplying secondary scrambling at a (transmission) symbol-level during arepetitive transmission duration. Here, primary scrambling of theRE-level includes scrambling data (e.g., codewords) at a bit-level or amodulation symbol-level. If primary scrambling of the RE-level includesscrambling at the modulation symbol-level, data may include data towhich scrambling at the bit-level is applied before primary scrambling.In addition, the specific time duration includes a time duration (e.g.,P subframes/slots) in which one data is transmitted. Here, thetransmission symbol includes an OFDM symbol or an SC-FDMA symbol. Thismethod may be applied to physical channels (e.g., NPDCCH, NPDSCH, andNPUSCH) repeatedly transmitted in the time domain.

Primary scrambling includes a process of applying a scrambling sequenceof a length of N or N*2 for N REs in one transmission symbol or applyinga scrambling sequence of a length of N*M or N*M*2 for N*M REs in onesubframe (or slot). Here, when the length of the scrambling sequence istwice the length of data, scrambling may be performed on an I/Q phase ofeach data RE. Initialization of the scrambling sequence for primaryscrambling may occur in the first transmission symbol (e.g., beginningof a subframe) or in the first subframe duration (e.g., start of a radioframe or the first subframe within a repeatedly transmitted subframeduration).

Table 12 illustrates a primary scrambling process of an RE-level.

TABLE 12 1) Get a block of complex-valued symbols (=modulation symbols)y^(p)(0), ... , y^(p) (K − 1)  K = number of complex-valued symbols in 1subframe (or slot) 2) The K complex-valued symbols to be transmitted isobtained as follows      {tilde over (y)}^(p)(i) = y^(p)(i)θ(i) Whereθ(i)is obtained as      ${\theta(i)} = \left\{ \begin{matrix}{{1\mspace{14mu}{if}\mspace{14mu}{c\left( {2i} \right)}} = {{0\mspace{14mu}{and}\mspace{14mu}{c\left( {{2i} + 1} \right)}} = 0}} \\{{{- 1}\mspace{14mu}{if}\mspace{14mu}{c\left( {2i} \right)}} = {{0\mspace{14mu}{and}\mspace{14mu}{c\left( {{2i} + 1} \right)}} = 1}} \\{{j\mspace{14mu}{if}\mspace{14mu}{c\left( {2i} \right)}} = {{1\mspace{14mu}{and}\mspace{14mu}{c\left( {{2i} + 1} \right)}} = 0}} \\{{{- j}\mspace{14mu}{if}\mspace{14mu}{c\left( {2i} \right)}} = {{1\mspace{14mu}{and}\mspace{14mu}{c\left( {{2i} + 1} \right)}} = 1}}\end{matrix} \right.$ And c_(j)(i) is a scrambling sequence initialized[at 1st subframe of repeated subframes (see, fugure 11)] by - c_(init) =(N_(ID) ^(Ncell) + 1)((10n_(f) + └n_(s)/s┘mod8192 + 1)2⁹ + N_(ID)^(Ncell) for NPDCCH - c_(init) = (N_(RNTI) + 1)((10n_(f) +└n_(s)/s┘mod61 + 1)2⁹ + N_(ID) ^(Ncell) for NPDSCH c(i),i = 0, ... ,2N −1 is given by    c(n) = (x₁(n + N_(C)) + x₂(n + N_(C)))mod2   x₁(n + 31)= (x₁(n + 3) + x₁(n))mod2   x₂(n + 31) = (x₂(n + 3) + x₂(n + 2) +x₂(n + 1) + x₂(n))mod2 where N_(C) = 1600 and the first m-sequence shallbe initialized with x₁(0) = 1,x₁(n) = 0,n = 1,2,...,30. Theinitialization of the second m-sequence is denotted by c_(init) =Σ_(i=0) ³⁰ x₂(i)·2^(i).

Secondary scrambling includes a process of performing scrambling at a(transmission) symbol-level while a transmission symbol or subframe towhich primary scrambling of the RE-level is applied is repeatedlytransmitted. Here, symbol-level scrambling is to perform the samescrambling for all REs during a (transmission) symbol duration and aspecific scrambling sequence is equally applied to all REs of a(transmission) symbol. That is, one value in a scrambling sequence maybe equally applied to N data (e.g., modulation symbols) or two valuesmay be equally applied to an I/Q phase. A sequence of secondaryscrambling may be generated using a value such as a cell ID (e.g.,N^(Ncell) _(ID)) and thus different scrambling sequences betweeninter-cells may be applied to the (transmission) symbol. In this case,the UE may descramble and then combine each (transmission) symbol in thetime domain before performing FFT for (transmission) symbols repeatedlytransmitted L times in L subframes. Therefore, since the UE may performRE-level descrambling after performing FFT only once, there is anadvantage that reception complexity does not increase.

Table 13 illustrates a secondary scrambling process of a (transmission)symbol-level.

TABLE 13 1) Get a block of complex-valued symbols (=modulation symbols)y₀ ^(p)(0), ... , y₀ ^(p) (M · N − 1)  M = number of OFDM symbols in asubframe  N = number of complex-valued symbols in an OFDM symbol (e.g.,N = 12) 2) The complex-valued symbols to be transmitted in a subframe #s(s = 1, ..., L−1) is obtained as follows    {tilde over (y)}_(s) ^(p)(i)= y₀ ^(p)(i)θ((s − 1) * M + └i/N┘) Where θ(l), q = 0, ... , M(L − 1) − 1is obtained as    ${\theta(l)} = \left\{ \begin{matrix}{{1\mspace{14mu}{if}\mspace{14mu}{c\left( {2l} \right)}} = {{0\mspace{14mu}{and}\mspace{14mu}{c\left( {{2l} + 1} \right)}} = 0}} \\{{{- 1}\mspace{14mu}{if}\mspace{14mu}{c\left( {2l} \right)}} = {{0\mspace{14mu}{and}\mspace{14mu}{c\left( {{2l} + 1} \right)}} = 1}} \\{{j\mspace{14mu}{if}\mspace{14mu}{c\left( {2l} \right)}} = {{1\mspace{14mu}{and}\mspace{14mu}{c\left( {{2l} + 1} \right)}} = 0}} \\{{{- j}\mspace{14mu}{if}\mspace{14mu}{c\left( {2l} \right)}} = {{1\mspace{14mu}{and}\mspace{14mu}{c\left( {{2l} + 1} \right)}} = 1}}\end{matrix} \right.$ c_(j)(i), i = 0, ... ,2M(L − 1) − 1 is ascrambling sequence initialized using a value associated with N_(ID)^(Ncell).

On the other hand, when data and a reference signal (e.g., NRS) aremultiplexed in one (transmission) symbol, since secondary scrambling isapplied only to the data descrambling/combining of a (transmission)symbol-level may not be performed for the corresponding (transmission)symbol. Therefore, when the reference signal is included in a specific(transmission) symbol, FFT should be performed for each (transmission)symbol and symbol-level descrambling and RE-level descrambling should beperformed at the RE-level in the frequency domain. In addition, the(transmission) symbol including the reference signal may be applied onlyto RE-level scrambling when another UE needs to use the referencesignal. However, when the reference signal is transmitted on all REs inthe (transmission) symbol or there is no data to be scrambled in thecorresponding (transmission) symbol, the above-described method may beapplied without change.

FIG. 14 illustrates a process according to Method #4 and an operationorder is as follows.

(1) One subframe consisting of N×M data (modulation) symbols may begenerated.

(2) A scrambling sequence generator may be initialized and a scramblingsequence having a length of N×M may be generated. When scrambling isapplied to an I/Q phase, a scrambling sequence having a length of N×M×2may be generated.

(3) Each data (modulation) symbol and sequence of (1) and (2) may bescrambled in one-to-one correspondence and mapped to N×M REs (primaryscrambling) (see Table 12).

(4) The scrambled first subframe may be copied into (L−1) subframes.Here, copying the subframe may be variously implemented as the meaningof repeatedly transmitting data of the first subframe in (L−1)subframes.

(5) A scrambling sequence having a length of M×(L−1) may be generated.In this case, one scrambling sequence value (e.g., 1/−1 or j/−j) may beequally applied to N REs (or modulation symbols) transmitted in one(transmission) symbol. When separately scrambling an I/Q phase, twosequence values may be used for one (transmission) symbol and ascrambling sequence having a length of M×(L−1)×2 may be generated. Inaddition, sequences used for (transmission) symbol-level scrambling maybe generated such that as different scrambling sequences as possible areapplied between inter-cells using a cell ID. In addition, the scramblingsequence having a length of M×L or M×L×2 may also be generated accordingto an implementation method. In this case, secondary scrambling may beapplied even to the first subframe in which data is transmitted.

(6) In unit of a (transmission) symbol of a subframe, a scrambling isperformed with a scrambling sequence in one-to-one correspondence(secondary scrambling) (see Table 13).

(7) L generated subframes may be sequentially transmitted. In this case,sequential transmission does not necessarily need to be consecutive inthe time domain. Here, transmitting the subframes means transmittingdata in the corresponding subframes.

[Method #5 Symbol-Level Interleaving]

Symbol-level interleaving proposed is a method of performing primaryscrambling of data at an RE-level and/or a (transmission) symbol-levelduring a specific time duration (see Tables 12 and 13) and thenperforming secondary interleaving for a transmission order of symbols atthe (transmission) symbol-level during a repeated transmission duration.Here, the data may include data to which scrambling is applied at abit-level before primary scrambling. The specific time duration includesa time duration (e.g., P subframes/slots) in which one data istransmitted.

The primary scrambling method includes performing scrambling at theRE-level and/or the (transmission) symbol-level for N*M data within asubframe duration. For example, primary scrambling includes a process ofapplying a scrambling sequence having a length of N*M or N*M*2 to N*MREs in one subframe (or slot). Here, when the length of the scramblingsequence is twice the length of the data, scrambling may be performedfor an I/Q phase of each data RE. Initialization of the scramblingsequence for primary scrambling may occur in the first transmissionsymbol (e.g., beginning of a subframe) or in the first subframe duration(e.g., start of a radio frame or the first subframe within a repeatedlytransmitted subframe duration).

Secondary (transmission) symbol-level interleaving is a procedure ofrandomly interleaving a (transmission) symbol transmission order withineach subframe when the first generated subframe (applied up to primaryscrambling) is repeatedly transmitted (L−1) times. In this case, therandomly interleaving method may be designed to maximally suppressinterleaving in the same order between inter-cells, based on a value ofa cell ID etc. In terms of inter-cell interference randomization, it maybe expected that this will not cause consecutive collision of therepeatedly transmitted same data between inter-cells. Particularly, in aslow-fading environment in which channel variation between repeatedlytransmitted subframes is not large, reception complexity of the UE maybe greatly reduced while performing inter-cell interferencerandomization by randomly interleaving a transmission order of(transmission) symbols using a cell ID based function within subframestransmitted L times. The UE may deinterleave and combine thetransmission order of the (transmission) symbols without performing FFTfor each of the (transmission) symbols repeatedly transmitted L timesand then performs RE-level descrambling in the frequency domain byperforming FFT once.

Table 14 illustrates a secondary interleaving process of a(transmission) symbol-level.

TABLE 14 1) Get a block of complex-valued symbols (=modulation symbols)y_(0,l) ^(p)(0), ... , y_(0,l) ^(p)(N − 1) M = number of OFDM symbols ina subframe N = number of complex-valued symbols in an OFDM symbol #1(e.g., N = 12) 2) The complex-valued symbols to be transmitted in asubframe #s (s = 1, ..., L−1) is obtained as follows {tilde over(y)}_(s,l) ^(p)(i) = y_(0,θ((s−1)*M+l)) ^(p)(i) Where θ(i), i = 0, ... ,M(L − 1) − 1 is a scrambling/interleaving sequence initialized using avalue associated with N_(ID) ^(N cell).

If a reference signal (e.g., an NRS) is included in a specific(transmission) symbol, since such (transmission) symbol-levelinterleaving may be restricted, other (transmission) symbol-levelinterleaving may be applied to some (transmission) symbols including thereference signal as follows. However, when the reference signal istransmitted in all (transmission) symbols or there is no data to bescrambled in the corresponding (transmission) symbols, theabove-described method may be applied without change.

(1) Interleaving is performed only for a data RE at a (transmission)symbol-level between (transmission) symbols including the referencesignal. In this case, although the UE may not perform deinterleaving anddescrambling by performing FFT once, inter-cell interferencerandomization may be expected. Even in this case, the UE may performcombining for (transmission) symbols without the reference signal bydeinterleaving a transmission order of the (transmission) symbols andthen perform descrambling of an RE-level in the frequency domain byperforming FFT once.

(2) Descrambling of the (transmission) symbol including the referencesignal may apply only RE-level scrambling or may use the scramblingmethod of Method #4. In addition, similar to Method #4, depending onwhether another UE that does not know whether the scrambling sequence isapplied to the reference signal needs to receive the reference signal,Method #5 is applied or only RE-level scrambling may be applied to the(transmission) symbol including the reference signal.

FIG. 14 illustrates a process according to Method #5 and an operationorder is as follows.

FIG. 15 illustrates an example of proposed scrambling Method #5.

FIG. 15 illustrates an example of proposed Method #5 and an operationorder is as follows.

(1) One subframe consisting of N×M data (modulation) symbols may begenerated.

(2) A scrambling sequence generator may be initialized and a scramblingsequence having a length of N×M may be generated. When scrambling isapplied to an I/Q phase, a scrambling sequence having a length of N×M×2may be generated.

(3) Each data (modulation) symbol and sequence of (1) and (2) may bescrambled in one-to-one correspondence and mapped to N×M REs (primaryscrambling) (see Table 12).

(4) The scrambled first subframe may be copied into (L−1) subframes.Here, copying the subframe may be variously implemented as the meaningof repeatedly transmitting data of the first subframe in (L−1)subframes.

(5) A scrambling sequence having a length of M×(L−1) may be generated.Here, the scrambling sequence is used in the same concept as thesequence for interleaving and is used to interleave the order of M(transmission) symbols in a specific subframe. The sequence forinterleaving the (transmission) symbol order may be different (persubframe) during L subframes and the (transmission) symbol order of thefirst subframe may be fixed to 0, 1, . . . , M−1. In addition, a cell IDetc. may be used to generate the sequence for interleaving the(transmission) symbol order, so that the (transmission) symbols may begenerated so as not to interleaved in the same order as much as possiblebetween inter-cells. In addition, the scrambling sequence having alength of M×L or M×L×2 may be generated according to an implementationmethod. In this case, secondary scrambling may be applied even to thefirst subframe in which data is transmitted.

(6) The (transmission) symbol order is interleaved according to thesequence generated within each subframe (secondary scrambling) (seeTable 14),

(7) The generated L subframes may be sequentially transmitted. In thiscase, sequential transmission does not necessarily need to beconsecutive in the time domain. Here, transmitting the subframe meanstransmitting data through the corresponding subframes.

The proposed “symbol-level scrambling and interleaving for inter-cellinterference randomization” method may be applied to both OFDMA andSC-FDMA schemes and may also be applied to other multiplexing ormultiple access schemes. In addition, the proposed method may be appliedto a single-carrier system other than a multi-carrier system and may beapplied regardless of DL, UL, and link direction. The proposed method isnot always applied only to inter-cell interference randomization and maybe used to randomize inter-used interference and inter-streaminterference. In particular, the proposed method may be used when thesame payload or information is repeatedly transmitted through a specificchannel and signal.

The proposed symbol-level scrambling and interleaving method may beadditionally applied separately from scrambling and interleaving appliedto bit-level and modulation (scheme such as QAM, PSK, FSK, or offsetQAM).

The proposed symbol-level scrambling and interleaving method serves torandomize inter-cell interference and elements used for randomization(e.g., variables/parameters used for a scrambling sequence/code ofsymbol-level scrambling or variables/parameters used for rearrangementof a transmission order of symbols in symbol-level interleaving) mayinclude a cell ID, a UE ID, and a stream order. In addition, valuesindicating time and frequency resources (e.g., a radio frame number, asubframe number, a slot number, a frequency index, and an RB index) maybe used as the elements for randomization. Random sequences (e.g., aGold sequence and an m-sequence) may be generated based on theabove-described randomization elements and symbol-level scrambling andinterleaving may be performed based on the random sequences. Forexample, each element of the scrambling code used for symbol-levelscrambling may be obtained from one, two, or more bits of a generatedrandom sequence. Here, each element of the scrambling code is multipliedby data at a (transmission) symbol-level and the multiplicationoperation may be a method of modulating the phase of a signal by aspecific phase in addition to simply changing only a sign. Thescrambling code used for (transmission) symbol-level interleaving maygroup the generated random sequence into N bits, select a value between0 and 2^(N)−1, and select a specific column and row in a table thatrandomly deploys transmission order rearrangement, thereby performingsymbol interleaving. This is simply illustrated as in FIG. 16. Referringto FIG. 16, it is assumed that each slot is repeatedly transmitted Mtimes and each slot includes 7 symbols. In this case, a random sequencefor symbol interleaving is generated using a cell ID and a slot numberand grouped in units of N bits. Since the N bits corresponding to thefirst slot in the random sequence represent 3, transmission symbols arearranged in order of {4, 1, 5, 0, 3, 6, 2}. In addition, since the Nbits corresponding to an M-th slot represent 1, the transmission symbolsare arranged in order of {0, 2, 3, 1, 4, 5, 6}. Here, the numbers inparentheses indicate transmission symbol indexes in a slot wheninterleaving is not applied.

The proposed “symbol-level scrambling and interleaving for inter-cellinterference randomization” method may be differently applied accordingto single-tone and multi-tone or may be differently applied according toa modulation scheme (e.g., BPSK, pi/2-BPSK, QPSK, or pi/4-QPSK).

For example, in the case of (transmission) symbol-level scrambling, forsingle-tone transmission (e.g., NPUSCH), a scrambling value for rotatingan I/Q phase may be limited to pi and −pi so as not to increase a PAPR.That is, in order to maintain an existing BPSK (or pi/2-BPSK) PAPR, I/Qphase rotation may be restricted to be performed only pi or −pi using a1-bit scrambling code (i.e., j and −j). On the other hand, forsingle-tone QPSK (or pi/4-QPSK) transmission, I/Q phase rotation may bedefined to be performed by pi/2, pi, pi/3, or 0 using a 2-bit scramblingcode (i.e., j, −1, −j, and 1). In a similar manner, in single-tone, therange and set of phase values capable of performing I/Q phase rotationmay vary according to a modulation method.

In (transmission) symbol-level interleaving, if a specific relationshipis needed between adjacent (transmission) symbols, such as pi/2-BPSK orpi/4-QPSK, (e.g., pi/2 differential, shift, or offset BPSK, or pi/4differential, shift, offset QPSK), even (transmission) symbols and odd(transmission) symbols may be separately interleaved in order tomaintain a corresponding characteristic. That is, interleaving may belimitedly performed only between even (transmission) symbols or betweenodd (transmission) symbols. In a similar way, if a specific relationshipis needed between one or more adjacent (transmission) symbols,interleaving may not be performed between (transmission) symbols (e.g.,N consecutive (transmission) symbols where N>1) that need to satisfy acorresponding characteristic and interleaving may be limitedly performedonly between (transmission) symbols having an interval of the Nconsecutive symbols or more.

FIG. 17 illustrates a BS and a UE of a wireless communication system,which are applicable to embodiments of the present disclosure.

Referring to FIG. 17, the wireless communication system includes a BS110 and a UE 120. When the wireless communication system includes arelay, the BS or UE may be replaced by the relay.

The BS 110 includes a processor 112, a memory 114 and a radio frequency(RF) unit 116. The processor 112 may be configured to implement theprocedures and/or methods proposed by the present disclosure. The memory114 is connected to the processor 112 and stores information related tooperations of the processor 112. The RF unit 116 is connected to theprocessor 112 and transmits and/or receives an RF signal. The UE 120includes a processor 122, a memory 124 and an RF unit 126. The processor122 may be configured to implement the procedures and/or methodsproposed by the present disclosure. The memory 124 is connected to theprocessor 122 and stores information related to operations of theprocessor 122. The RF unit 126 is connected to the processor 122 andtransmits and/or receives an RF signal.

The embodiments of the present disclosure described hereinbelow arecombinations of elements and features of the present disclosure. Theelements or features may be considered selective unless otherwisementioned. Each element or feature may be practiced without beingcombined with other elements or features. Further, an embodiment of thepresent disclosure may be constructed by combining parts of the elementsand/or features. Operation orders described in embodiments of thepresent disclosure may be rearranged. Some constructions of any oneembodiment may be included in another embodiment and may be replacedwith corresponding constructions of another embodiment. It will beobvious to those skilled in the art that claims that are not explicitlycited in each other in the appended claims may be presented incombination as an embodiment of the present disclosure or included as anew claim by a subsequent amendment after the application is filed.

In the embodiments of the present disclosure, a description is madecentering on a data transmission and reception relationship among a BS,a relay, and an MS. In some cases, a specific operation described asperformed by the BS may be performed by an upper node of the BS. Namely,it is apparent that, in a network comprised of a plurality of networknodes including a BS, various operations performed for communicationwith an MS may be performed by the BS, or network nodes other than theBS. The term ‘BS’ may be replaced with the term ‘fixed station’, ‘NodeB’, ‘enhanced Node B (eNode B or eNB)’, ‘access point’, etc. The term‘UE’ may be replaced with the term ‘Mobile Station (MS)’, ‘MobileSubscriber Station (MSS)’, ‘mobile terminal’, etc.

The embodiments of the present disclosure may be achieved by variousmeans, for example, hardware, firmware, software, or a combinationthereof. In a hardware configuration, the methods according to theembodiments of the present disclosure may be achieved by one or moreApplication Specific Integrated Circuits (ASICs), Digital SignalProcessors (DSPs), Digital Signal Processing Devices (DSPDs),Programmable Logic Devices (PLDs), Field Programmable Gate Arrays(FPGAs), processors, controllers, microcontrollers, microprocessors,etc.

In a firmware or software configuration, the embodiments of the presentdisclosure may be implemented in the form of a module, a procedure, afunction, etc. For example, software code may be stored in a memory unitand executed by a processor. The memory unit is located at the interioror exterior of the processor and may transmit and receive data to andfrom the processor via various known means.

Those skilled in the art will appreciate that the present disclosure maybe carried out in other specific ways than those set forth hereinwithout departing from the spirit and essential characteristics of thepresent disclosure. The above embodiments are therefore to be construedin all aspects as illustrative and not restrictive. The scope of thedisclosure should be determined by the appended claims and their legalequivalents, not by the above description, and all changes coming withinthe meaning and equivalency range of the appended claims are intended tobe embraced therein.

INDUSTRIAL APPLICABILITY

The present disclosure is applicable to UEs, eNBs or other apparatusesof a wireless mobile communication system.

The invention claimed is:
 1. A method of transmitting a signal by a basestation (BS) in a wireless communication system, the method comprising:generating a first complex symbol sequence related to one time unitincluding a plurality of transmission symbols; generating a secondcomplex symbol sequence by applying primary scrambling to the firstcomplex symbol sequence in units of modulation symbols; and repeatedlytransmitting the second complex symbol sequence through a plurality oftime units, wherein secondary scrambling is applied to a signal in eachtime unit in units of transmission symbols by multiplying one valueamong a plurality of complex values, in units of the transmissionsymbols, to the signal in each time unit, wherein the transmissionsymbols include orthogonal frequency division multiplexing (OFDM)symbols or single-carrier frequency division multiple access (SC-FDMA)symbols.
 2. The method of claim 1, wherein the second complex symbolsequence is transmitted through a narrowband physical downlink controlchannel (NPDCCH), a narrowband physical downlink shared channel(NPDSCH), or a narrowband physical uplink shared channel (NPUSCH). 3.The method of claim 1, wherein the time unit includes a slot.
 4. Themethod of claim 1, wherein the second complex symbol sequence istransmitted through 1, 3, 6, or 12 subcarriers in each time unit.
 5. Themethod of claim 1, wherein the order of the transmission symbols of thesignal changes for each time unit.
 6. The method of claim 1, wherein thewireless communication system includes a wireless communication systemsupporting narrowband Internet of Things (NB-IoT).
 7. A user equipment(UE) used in a wireless communication system, the UE comprising: atransmitter and a receiver; and at least one processor; and at least onecomputer memory operably connected to the at least one processor andstoring instructions that, based on being executed by the at least oneprocessor, perform operations comprising: generating a first complexsymbol sequence related to one time unit including a plurality oftransmission symbols, generating a second complex symbol sequence byapplying primary scrambling to the first complex symbol sequence inunits of modulation symbols, and repeatedly transmitting the secondcomplex symbol sequence through a plurality of time units, whereinsecondary scrambling is applied to a signal in each time unit in unitsof transmission symbols by multiplying one value among a plurality ofcomplex values, in units of the transmission symbols, to the signal ineach time unit, and wherein the transmission symbols include orthogonalfrequency division multiplexing (OFDM) symbols or single-carrierfrequency division multiple access (SC-FDMA) symbols.
 8. The UE of claim7, wherein the second complex symbol sequence is transmitted through anarrowband physical downlink control channel (NPDCCH), a narrowbandphysical downlink shared channel (NPDSCH), or a narrowband physicaluplink shared channel (NPUSCH).
 9. The UE of claim 7, wherein the timeunit includes a slot.
 10. The UE of claim 7, wherein the second complexsymbol sequence is transmitted through 1, 3, 6, or 12 subcarriers ineach time unit.
 11. The UE of claim 7, wherein the order of thetransmission symbols of the signal changes for each time unit.
 12. TheUE of claim 7, wherein the wireless communication system includes awireless communication system supporting narrowband Internet of Things(NB-IoT).